The present invention relates to a method and apparatus for treating a permeable web material with a fluid. The fluid may be used for displacement washing of the web, it may be a reactive material such as a bleach or dye, or it may be some other type of treatment.
A number of different generic types of apparatus are known for treatment of woven or non-woven webs with various fluid materials. One very common type is the vacuum drum. Here a web of material is run onto the porous surface of a drum and fluid is flowed onto the material from external showers. Vacuum boxes or other means for creating a reduced pressure within the drum draw the fluid through the web. Alternatively, the web may be formed on the drum from a slurry of fibrous material prior to treatment. One or more press rolls may bear against the drum to assist in fluid removal. An alternative but similar form of apparatus uses a shroud enclosed drum which is pressurized on the outside. In this case the pressure is generally quite low, typically in the range of 15 to 30 kPa. In another type of treatment apparatus the web is held between two fluid permeable parallel wires supported on or between a series of small diameter press rolls. Fluid can be showered on the web between the press rolls.
To show some specific examples of apparatus for treating permeable webs, Sando et al., U.S. Pat. No. 4,277,860, show a woven cloth carried between opposing fluid permeable belts immersed in a treating fluid. Staggered opposing nozzles placed under the fluid and outside the belts spray hot fluid onto both surfaces of the cloth as it passes through the fluid bath.
Lintunen et al., U.S. Pat. No. 4,292,123, show a washer for a continuous web of cellulose pulp. The pulp is formed into a wet sheet or mat on a simple forming wire prior to contacting the outer surface of a fluid permeable rotating drum. The drum is surrounded by a plurality of washing stations which are spaced a sufficient distance from the drum surface to accommodate the pulp web. Washing fluid is introduced, preferably in countercurrent fashion, where it then flows through a foraminous surface in the washer stations, through the pulp, and then into a collection zone into the interior of the drum.
Walsh, U.S. Pat. No. 3,199,317 shows a fabric or similar material being carried on a moving endless belt having a concave portion dipping into a pool of treating fluid. The fabric emerges from the bath and passes, while still on the belt, between a pair of rollers that squeeze out excess fluid.
Winch, U.S. Pat. No. 4,199,966, show a web being carried on an endless perforated belt through a tank of fluid. A series of rollers are placed alternately above and below the belt so that it travels a somewhat sinuous path. As the web on the belt passes under a roller it is lightly squeezed. As the belt passes over the adjacent roller the web expands. Fluid may be passed through the tank in countercurrent fashion to effect washing or other treatment.
Many of the devices just described, while being well suited for some specific purpose for which they were designed, have serious shortcomings when used with other materials or for different types of treatments. Among these shortcomings are the need for large quantities of treating fluid, with attendant expensive collection and pumping equipment, and discharging a treated mat which is still very wet and contains a large amount of entrained treating fluid.
My earlier U.S. patent application, Ser. No. 849,931, filed Apr. 8, 1986, is hereby incorporated by reference. There are certain common features shared by the pressing device of the earlier application and my present apparatus which is used for treatment of a permeable mat with a fluid. The earlier described device is not suitable for the latter purpose without the major modifications and improvements now to be described.